Fatty amines as color stabilizers for dialkyl phthalates



United States Patent ABSTRACT OF THE DISCLOSURE A color-stable composition comprising a dialkyl ester of a phthalic acid containing a color stabilizing amount of a fatty amine having the formula R NH wherein x is an integer of 1 or 2 and R is an aliphatic group containing from 12-24 carbon atoms.

This invention relates to the color stabilization of dialkyl phthalates which are normally subject to discoloration due to the influence of heat, oxygen, metals and/or aging. More particularly, this invention relates to the use of fatty amines to stabilize dimethyl terephthalate and other dialkyl phthalates against discoloration.

The use of phthalic acid diesters as plasticizers for resinous compositions and as starting materials in the preparation of polyester resins is Well known in the art. However, one objection to such compounds is that they tend to, become discolored under certain conditions, such as when subjected to the influence of heat, oxygen, metals and/or aging.

It is an object of this invention to provide an effective color stabilizer for dialkyl phthalates such as dimethyl terephthalate.

It is another object of this invention to provide a dialkyl phthalate composition containing an amine stabilizer which is effective at levels as low as 1 to 5 parts per million.

It is a further object of this invention to provide a dialkyl phthalate composition which will not become discolored when subjected to the influence of heat, oxygen, metals and/or aging.

These, and other objects, are attained by the practice of this invention which, briefly, comprises providing a composition comprising a dialkyl ester of a phthalic acid having the formula COOR COOR

wherein each R is an alkyl group containing from 1 to 6 carbon atoms, said composition containing a color stabilizing amount of a fatty amine having the formula R NH wherein x is a whole integer having a value of from 1 to 2 and R is an aliphatic group containing from 12 to 24 carbon atoms. This composition is characterized by being stable against discoloration when sub jected to the influence of heat, oxygen, metals and aging.

The dialkyl esters of phthalic acid which may be color stabilized in accordance with the practice of this invention include the lower (alkyl) esters of the ortho, meta and para isomers of phthalic acid. Such compounds include dimethyl phthalate, dibutyl phthalate, dimethyl isophthalate, diethyl isophthalate, di-n-butyl isophthalate, dimethyl terephthalate, diethyl terephthalate, di-n-propyl terephthalate, di-n-butyl terephthalate, etc.

The amines which may be used to stabilize the dialkyl phthalates according to this invention are primary or secondary fatty amines (i.e., R Nl-l or R NH) in which the aliphatic R group or groups such as straight or branch chain contain from 12 to 24 carbon atoms. Such compounds are well known and are commercially available under a variety of trade names. These products contain either predominantly one aliphatic chain length or mixtures of several aliphatic chain lengths. Some examples of such commercially available primary and secondary fatty amines include Primene 81-R (a primary fatty amine having a boiling point of from 221 to 238 C. and a neutral equivalent of 191 in which the aliphatic group comprises a mixture of t-alkyl isomers having from 12 to14 carbon atoms); Primene J MT (a primary fatty amine having a boiling range of from 265 to 305 C. and a neutral equivalent of 330 in which the aliphatic group comprises a mixture of t-alkyl isomers having from 18 to 22 carbon atoms); Alamine 205 (ditetradecyl amine having a melting point of 52 C.); and Alamine 207 (dioctadecyl amine having a melting point of C.).

The fatty amine may be used in an amount as low as 1 part per million to stabilize the dialkyl phthalates although it is preferred to use it in an amount of at least 5 parts per million. It is also preferred that the fatty amine be used in an amount less than about 260 parts per million since higher concentrations tend to accelerate rather than retard color formation.

The fatty amine may be added to and mixed with the dialkyl phthalates in any convenient manner. Since the fatty amine is used in such small amounts as compared to the amount of dialkyl phthalate, it is generally advantageous to add it in the form of a dilute stock solution of the fatty amine in order to avoid Working with minute quantities of the fatty amine.

The color stabilized dialkyl phthalate compositions may be used in the manner well known in the art for utilizing dialkyl phthalates. That is, they may be used as plasticizers or in condensation reactions with glycols in the preparation of linear polyesters such as polyethylene terephthalate.

The following examples illustrate the best modes contemplated for carrying out this invention:

EXAMPLES 1 TO 8 In these examples, a series of the fatty amines listed in Table 1 were tested as color stabilizers for dimethylterephthalate. Solutions containing 0.01 g. of each amine in 50 ml. of acetone were first prepared. A quantity of each solution was pipetted into a 10 in. tube having a diameter of /s-inch containing 20 g. of unstabilized dimethyl terephthalate in an amount sufiicient to provide the concentration of the amine indicated in Table 1. (One ml. of the stock solution imparts 10 ppm. of the amine to the 20 g. sample of dimethyl terephthalate.) The tube was then placed in an electrically heated aluminum block which was preheated to a temperature of 165 C. and aged. At intervals during the aging, the dimethyl terephthalate samples were matched with a set of APHA color standards. The time required for a sample to reach an APHA color rating of 25, 50 and/or is recorded in 3 4 Table 1. The results of the tests set forth in Table l indiinherent viscosities of about 0.25 as measured in a 60% cate that dimethyl terephthalate containing 10, 20 and phenol-40% tetraehloroethane solution.

TABLE 2 Goncen- Hrs. Dlmethyl APHA Color Pre 01 e Example Amine tratlon, Terephthalate of Dlmethyl c ialoi r p.p.m. Aged at 156 0. Terephthalate Rating after Aging 9 None 50 50 3 10 Alamlne 205 635 60 1 l1 0 467 60 1 12 Prlmene 81-12.. 20 138 50 1 13 Primene J WT... 20 170 50 1 50 ppm. of a fatty amine are considerably more resist- 15 Other alkyl esters of phthalic acid, isophthalic acid ant to discoloration by heat than is dimethyl terephthalate and terephthalic acid may be stabilized with fatty priwhich contains no fatty amine; and that the use of 200 mary and secondary amines employing the procedures p.p.m. of fatty amine accelerates rather than retards the set forth in the preceding examples and in the more heat discoloration of dimethylterephthalate. general description set font}; h m b TABLE 1 Stability at 165 C. Concentra- Initial xam le Amine tion p.p.m. APHA Hr. to Hr. to Hr. to E p Color APHA APHA APHA of 0f 50 of 75 7.... 0 8 Primenesl-R EXAMPLES 9 TO 13 We claim:

1. A composition comprising a dialkyl ester of a These examples illustrate the use of fatty anune stah h li id having the f r la bilized dimethyl terephthalate to prepare prepolymers 000R of poly (l,4-dimethylenecyclohexylene terephthalate). l

By the process described in the preceding examples, there were added the amounts of the amines listed in Table 2 000R to portions of dimethyl terephthalate and these portions were aged at 165 C. for the times indicated in Table 2.

The APHA color of the dimethyl terephthalate after wherein each R is an alkyl group containing from 1 to 6 aging at for the i time is sat forth in carbon atoms, said composition containing a color sta- Table 2. Each of the POIUOIIS. of dimethyl terelphthalate bum-mg amount of a fatty amine having the formula g-; mole) was admixed Wlth Ohexane' R NH wherein x is a whole integer having a value dim tha 8-; 0-014 molt?) f 1 f of M of firom 1 to 2 and R is a straight or branch chain alkyl catalyst. Thls mlXtllfe Was mated "3 a F containing from 12 to 24 carbon atoms, said composition steel in a glass test tube equipped with a distillation head being charadterized by being Stable against discoloration and a mtrogen inlet tubeat 200 C. for 15 minutes and when subjected to the influence of heat, oxygen mctals then at 310 C. for 20 nnnutes A h l was d aging,

applied to the system and heatmg was continued at 310 A composition as defined in claim 1 wherein said C. under a pressure of 0.08 mm. of Hg for 10 mmutes. fatty amine is a primary amine having the formula The color of the melt of the resultant prepol ymers was R1NH2 observe immediatfily aflleT heatmg was dlscontmued 3. A composition as defined in claim 1 wherein said using APHA color standards. A color rating 9 m 1 fatty amine is a secondary amine having the formula to 8 was assigned to each polymer. The relatlonslnp of RIZNH the color rating to the APHA color of the melt is as A composition as defined in claim 1 wherein Said fOllOWS- fatty amine is present in said composition in an amount Color Iatm'g of from 10 to 50 parts per million.

Me11lC010T(APHA): of prcpolymg'r 5. A composition as defined in claim 1 wherein said 045 1 di lkyl ester of a phthalic acid is dimethyl terephthalate, 25-375 2 3 References Cited $2118 j j j j 21$ nose a an Condensed Chem. Dictionary, Reinhold, 1 0 5 'IIIIIIIIIIQ M New York, NY, 1956, 6th p- 2 The color Tating of the prepolymer Obtained in each LORRAINE A. WEINBERGER, Primary Examiner. example is indicated in Table 2. The prepolymers had T. L. GALLOWAY, Assistant Examiner. 

